This invention relates to an apparatus and method for treating wastewater, particularly to an apparatus and method for treating wastewater that is capable of handling not only ordinary, everyday flow rates and pollutants of wastewater, but also achieving similar or better treatment during surge periods and/or wet weather conditions.
In a typical wastewater treatment plant, wastewater is treated through a series of removal processes. One such removal process is settling or clarification. It is in this treatment step that many of the heavier solids (or materials with a specific gravity greater than one) are settled out of wastewater. It is typical for conventional clarifier basins to be sized for hydraulic settling rates of around 0.5 to 1.5 gpm/ft2.
To produce a better clarifier effluent quality, chemically enhanced clarification-settling has been developed and implemented in many plants around the world. Coagulants and/or flocculants react and condition the influent water, which in turn increases the specific gravity of the incoming solids. These denser solids settle out more rapidly and, therefore, allow for more aggressive flow rates and smaller clarifier basins. One example of this technology is the Accelator(copyright) Clarifier.
To further assist in the settling of these particles, it is possible to add and/or recirculate a xe2x80x9cballastxe2x80x9d material to mix with the incoming solids. This ballast material is typically sludge or sand. Unlike conventional clarifiers, these high rate clarification systems are of a significantly smaller footprint (possibly 5 to 10 times smaller), and they consistently produce equal or better quality effluent. The main drawback to ballasted high rate clarifiers is that they have higher operational costs, including increased power and maintenance costs, and chemical requirements. Examples of this technology include the DensaDeg(copyright) Clarifier or the Actiflo(copyright) Clarifier. It should be noted that because these high-rate clarifiers are of a significantly smaller footprint than conventional clarifiers, they cannot achieve conventional effluent quality without the use of chemicals, operating at the same flow rate.
A further problem facing existing wastewater treatment plants is that they have been sized to meet wastewater flow conditions, which may be completely inadequate during high flow occurrences, such as during heavy periods of rain. In such instances, the flow of wastewater may receive inadequate treatment, depending on the capacities and capabilities of the individual wastewater treatment plant. Some plants must bypass their treatment processes with this wet weather flow.
An alternative to address this situation is to provide for an increased size of the wastewater plant sufficient to handle such peak flows. However, in such instances, a significant, if not a majority of the capacity of the plant remains unused for the vast majority of the time. Clearly, this provides for serious inefficiencies and underutilization of facilities that are quite expensive from the standpoint of capital and operating cost.
A further alternative has been to construct storage basins/tunnels to essentially hold the peak wastewater volumes until the excess can be treated over the course of time. Again, this requires a significant capital commitment and also uses large areas/volumes of space, oftentimes which are not available because of space constraints.
Accordingly, it would be highly advantageous to provide a system and method capable of treating wastewater in a cost-efficient manner that can clarify normal design flow and pollutant levels, but also is flexible enough to handle peak events so as to avoid large storage facilities and maintain a small footprint.
The invention relates in one aspect to an apparatus for treating wastewater that includes a physical-chemical reaction vessel or reactor and a chemical supply operably connected to the physical-chemical reaction vessel. A clarifier operably connects to and is located downstream of the physical-chemical vessel. A ballast recirculation line is operably connected between the clarifier and the high rate physical-chemical vessel. Finally, the apparatus includes a control system that directs a) influent into 1) the clarifier but not the physical-chemical vessel when influent conditions are within a selected low range and 2) the physical-chemical vessel and then into the clarifier when the influent conditions are within a selected higher range, and b) ballast from the clarifier into the physical-chemical vessel through the sludge recirculation line when the flow or pollutant loading is within the selected higher range.
The invention also includes a method of treating a variable flow/pollutant loading of wastewater that includes removing selected materials from the wastewater. During a normal flow or pollutant loading of wastewater, the wastewater is typically 1) subjected to clarification in a clarifier without the use of coagulating/flocculating chemicals, 2) biological treatment and possibly 3) settling and/or filtration and/or disinfection. During an increased flow or loading of wastewater, 1) coagulant, and possibly flocculant, is added to the incoming wastewater, 2) ballast within the clarifier is recirculated into the resulting mixture, 3) the resulting mixture is subjected to agitation in a physical-chemical vessel, and 4) the resulting mixture is subjected to settling in the clarifier. Clarifier effluent may then be subjected to biological treatment, settling, filtration, and disinfectionxe2x80x94or any combination thereof.